Mental Exhaustion

Mental fatigue — feeling cognitively drained, slow and unable to concentrate — is usually the sum of sleep debt, sustained stress, decision overload and too little recovery, rather than a supplement deficiency. It is worth ruling out common medical contributors: iron deficiency (with or without anaemia), underactive thyroid, low mood and poor sleep quality including apnoea. Caffeine masks fatigue short-term but fragments sleep when taken after mid-afternoon. Rhodiola rosea (200-400 mg of standardised extract) has modest trial support for stress-related fatigue; the foundation remains sleep regularity, workload boundaries and genuine breaks.

Evidence synthesis: Rhodiola rosea has the strongest evidence base among adaptogens for fatigue, with several randomised trials showing reductions in mental fatigue and improvements in attention under stress, including in burnout populations — though many trials are small and some originate from research groups with commercial ties. Creatine has emerging evidence for reducing mental fatigue during cognitively demanding tasks and sleep deprivation. For the common causes themselves, the evidence is unambiguous: sleep restriction reliably impairs cognition, depression presents with fatigue in most cases, and iron deficiency without anaemia causes measurable fatigue that resolves with repletion. No supplement substitutes for reducing workload or restoring sleep.